Vulcanization of rubber



Patented Feb. 3, 1942 VULCANIZATION F RUBBER Arthur W. Sloan, Akron,Ohio, assignor' to The B. F. Goodrich Company, New York, N. Y., acorporation of New York No Drawing. Application December4, 1937, SerialNo. 178,111

14 Claims. ((1260- 785) The present invention relates to thevulcanization of rubber and rubber-like materials, and to improvementsin the process of vulcanization.

Of the large number of accelerators of vulcanization which have founduseful. application,

none has been universally applicable, so great and varied are thedemands made upon them. It has been found possible to improve thevulcanizates which can be obtained by the use of accelerators by usingthem in combination with other materials which may be called activatorsof the accelerators. These materials of themselves may be mildaccelerators, but in general they have little accelerating power Whenused alone.

I have found that an especially useful type of activator is thatcomprising the class of primary Z-amino thiazoles, such as Z-aminothiazole, 2- amino 4-methy1 thiazole, Z-amino 4-ethyl thiazole, Z-amino4.5 dimethyl thiazole, 2-amino 4- phenyl thiazole, 2-amino-4-p-ethoxypheny1 thiazole, Z-amino 4-phenyl 5-methyl thiazole,2-aminobenzothiazole, 2-amino 4 methyl benzothiazole, Z-amino G-methoxybenzothiazole, Z-amino alpha-naphthothiazole, 2-aminobeta-naphthothiazole, and 2.2 diaminobenzodithiazole. These compoundsall have the general structure represented by the following formula:

'in which A and B represent hydrogen or aliphatic or aromatic radicalsor a bivalent radical forming with the two adjacent C atoms a homocyclicring. Those compounds in which A and B unite to form an aromatic ringfused with the thiazole ring, such as benzothiazole, naphthothiazole,etc., are frequently called for convenience arylene-thiazoles. Thecorresponding amino oxazoles, in place of amino thiazoles, are likewiseuseful.

None of these materials has heretofore been suggested as an activatorfor accelerators of vulcanization. One of them has been tried as anaccelerator, but with negative results. For ex: ample, Sebrell (Ind. andEng. Chem. 15, 1013 (1923)) compared Z-aminobenzothiazole as anaccelerator, with Z-mercaptobenzothiazole, and found the aminobenzothiazole to be a very weak thiazoles are very effective inincreasing the activity of other active accelerators of vulcanization.

I have also found that certain ofthe aminothiazoles, i. e. those inwhich the thiazole ringv is not fused with an aromatic ring such as abenzene ring, are active accelerators in their own right. This is allthe more surprising when it is considered that Sebrell, in the articlereferred to above, concluded that omission of the benzene rin ofmercaptobenzothiazole, or substitution of an amino group for themercapto group, reatly diminished the activity of the compound. It nowappears that both changes when made concurrently, instead'of having acumulative effect in diminishing activity, actually restore theaccelerating power ofthe compounds.

These materials can be made in a variety of ways, for example byreacting the corresponding Z-chlorderivative with ammonia preferably atan elevated temperature, with or without a diluent such as benzene oralcohol. They may. also be made by reacting alpha chlor substitutedketones or aldehydes with thiourea. Phenacyl chloride, for example,reacts readily with thiourea in aqueous suspension or in alcoholsolution to form 2 -amino 4 phenyl: thiazole. Amino benzo thiazole canbe formed in good yield by reacting an excess of ammonia with 2chlorbenzothiazole in methyl alcohol solution, under pressure at anelevated temperature. It can also be formed by oxidizing mono-phenylthiourea in benzene with an oxidizing agent such as chlorine or bromine,with subsequent neutralization of the acid formed in the reaction.

Other amino thiazoles have been prepared, largely for use asdyeintermediates, by the above or other methods, and may be founddescribed in British Patent 295,295; British Patent 347,141; FrenchPatent 688,867; German Patent 537,105; and United States Patents1,787,315; 1,787,316; and 1,788,297.

The following examples are given of the use of certain of these aminothiazoles in rubber vulcanization where mercaptobenzothiazole is used asthe accelerator.

In a rubber composition containing rubber 100 parts, zinc oxide 8 parts,channel carbon black beta naphthyl amine 0.75 part, and2-mercaptobenzothiazole 0.5-0.9 part as indicated, the addition of theamino thiazoles listed in the table below had. the efiects noted in thetable, on the accelerator. Nevertheless the primary, Z-amino rate ofcure at 220 F. and at 265'F., and on the Z-mercapto 4,5 dimethylthiazole.

The generic term a rubber is meant to designate generally rubberymaterials susceptible of Mermp I Tensile of Tensile tobenzo Aminothiazole ggg g 'i'go :521? thiazole F. aging 0. 9 None 2, 075 0.9 0.22-aminobenzothiazole 2, 400 0. 9 0.4 Z-amino 4.5-dimetl1yl- 3, 025

thiazole. 0. 7 0.4 2-amino 4.5-dimethyl 2, 940

thiazole. 0.9 0.2 2aminotl1iaz0le 2,900 0.5 0.4 2-aminothiazole 2, 3000. 9 0.2 2-amino 4-ethylthiazole 2, 750 0. 9 0.4 Z-amino4-phenylthiazole. 2, 780

It will be noted that the rate of vulcanization has been increased bythe addition of the aminothiazole and that by its use, the amount 'ofaccelerator can be reduced without lowering the rate of vulcanization;also that the ultimate tensile strength of the rubber is increased, thatthe increased rate of vulcanization and improved tensile strength areaccomplished without increasing the scorchiness of the rubber mixturei.e. the tendency to precure as reflected by the rate of vulcanization at220 F.-and that the vulcanizates containing the aminothiazoles agebetter in the Bierer-Davis bomb at 70 C. 'under 300 lbs. oxygen pressurethan do the vulcanizates lacking the amino thiazoles. Similar resultsare secured with other mercaptothiazoles,

particularly the mercapto alkylthiazoles such as Other activeaccelerators, such as the esters of mercaptobenzothiazole, thealdehyde-amines, the guanidines and the thiurams (salts, esters,sulfides, etc.) are likewise activated by these materials, but ingeneral the so-called basic accelerators such as the guanidines andaldehydeamines are less sensitive to their presence than the so-calledacidic type of accelerator including the mercaptothiazoles, as well asother mercaptosubstituted organic bases such as 'mercaptoquinoline, andthe accelerating thio acids such as dithiobenzoic acid, xanthogenicacids, dithiocarbamic acids and the like, and salts, esters, acidanhydrides, disulfides, and other derivatives of the types well known tobe active accelerators of vulcanization, of any of them,

These amino thiazoles in which the thiazole ringe is not fused with anaromatic ring are useful alone as accelerators. For example, 2-aminothiazole, 2-arnino 4-methyl thiazole, 2-amino 4-ethyl thiazole, and2-amino 4,5-dimethyl thiazole are accelerators of moderate activity asindicated by the following data:

A rubber composition containing rubber 100 parts, zinc oxide 10 parts,sulfur 3.5 parts, barytes parts, and 2-aminothiazole 1 part, whenvulcanized for 90 min. at 287 F. gave a vulcanizate having a tensilestrength of 3455 lbs/sq. in. and an ultimate elongation of 700%.

In contrast with this result, a rubber composition containing rubber 100parts, zinc oxide '10 parts, sulfur 4 parts, and anilinobenzothiazole 1part, when vulcanized for 90 min. at 287 F. gave a vulcanizate having atensile strength of only 1465 lbs/sq. in., and an ultimate elongation of965%, indicating that very little cure had taken place.

By replacing the anilinobenzothiazole with 2-aminobenzothiazole, atensile strength of 1890 lbs/sq. in., and an ultimate elongation of 880%were obtained.

vulcanization with sulfur, such as caoutchouc, abalata, gutta percha,natural or artificially prepared latex, and synthetic rubber.

It is to be understood that the activators may beused in admixture withantioxidants, softeners, pigments, fillers, etc. and that the rubber maybe vulcanized with the assistance of this new class of activators inother manners than that particularly set forth above; specifically, itmay be vulcanized in hot air, steam, hot water, etc. The activators maybe advantageously employed in small proportions, usually not more than1% of the rubber in the compositions. Amounts as high as 5% or over maybe used, however.

For the purposes of this patent, the two isomeric formulas ar consideredas being equivalent or identical.

The'scope of this invention is not to be limited to the specificexamples herein set forth, but is to belimited only as required by theprior art and as indicated in the appended claims.

I claim:

1. The process of vulcanizing a rubber in the presence of an activeaccelerator of vulcanization of the acidic type and as an activatortherefor a primary 2-amino thiazole.

2. The process of vulcanizing a rubber in the presence of an activeaccelerator of vulcanization of the acidic type and as an activatortherefor 2-amino benzothiazole.

3. The process of vulcanizing a rubber in the presence of 2-mercaptobenzothiazole and as an activator therefor 2-amino benzothiazole.

4. The process of vulcanizing a rubber in the presence of a primary2-amino thiazole in which the thiazole ring is not a part of a fusedring system.

5. The process of vulcanizing a rubber in the presence of a primaryZ-amino alkyl-substituted thiazole.

6. The process of vulcanizing a rubber in the presence of an activeaccelerator of vulcanization of the acidic type and as an activatortherefor a primary Z-amino thiazole in which the thiazole ring is not apart of a fused ring system.

7. The process of vulcanizing a rubber in the presence of an'accelerating mercapto heterocyclic base and as an activator therefor aprimary 2-amino thiazole.

8. The process of vulcanizing a rubber in the presence of aZ-mercaptothiazole and as an activator therefor and a primary 2-aminothiazole.

9. The process of vulcanizing 'a rubber in the presence of a2-mercapt0thiazo1e and as an activator therefor Z-aminothiazole.

10. The process of vulcanizing a rubber in the presence of a Z-mercaptoalkylthiazole and. as an activator therefor 2-amino alkylthiazole.

11. A rubber composition comprising a rubber which has been vulcanizedin the presence of an active accelerator of vulcanization of the acidictype and as an activator therefor a primary 10 Z-aminoalkyl thiazole.

12. A rubber composition comprising a rubber CERTIFICATE OF CORRECTION.Patent No. 2,271,782. February 5, 19h2.

ARTHUR w. sLoAN'.

It is hereby'qerfiified that error appafs in the printed S e ificatiOnoffhe above numbe r 'ed patent requiring gorrection'aafqllow: Page 2,first column, 11ne 50., for the word ,"T hese".re ad' '-Thos e-'-; line513 for "ringe" re ad "ring"; and second cblumn 1: [ne 17', forfabalataWnead --ba1ata--; line 711., 0151 118, Strikeout "and" after "'therec r"'; pag'eE, second dolumn,

line 5, claim '12, 01 ts? read --'is-'-;; and tht tn sRidLettz-s'mvcent'should be read with this cd rf'e u 6n thereimthat [the sme may conformto the'record of the case in the Patent office.

Signed and sealed this 1st day of Deqe mb r, D. 19142.1

Henry Van Arsdal'e (Seal) Acting comr'nissidngr o f Patent s,

